I've looked at the FAQ, but I wondered if anyone would be able to specifically identify the most likely fault with my car.

It's an '84 1272cc HK, completely standard.

I have an intermittent hesitation/loss of power which occurs when driving at speed (but not any particular speed). It happens infrequently and is therefore impossible to reliably recreate.

Just from listening to the engine (no rev counter) I think it's idling a bit fast (but not much, maybe 100-200rpm) and I also think my fuel consumption might be slightly high (I suspect these might be related). I haven't attempted to calculate my mpg, but I just got 200 miles off a tank doing mostly fast A-road driving (i.e. 50-60mph) and I think this is a bit poor. My Scirocco 1.8i was doing 36mpg on the same run.

I'm waiting for a Haynes to arrive so that I can try to set up the carb properly and I think I should take a look at the points to see if they're set properly.

I don't have any problems with cold or hot starting and idling is steady, just fast.

If the problem seems like an obvious fault, please let me know what you think it is.

I think we need some more symptoms.

I guess:

It doesn't misfire or cut-out... then I'll stick my neck out and say it's probly not electrical.

I assume:

It's not overheating.

The autochoke works.

Could be a carb jet partially blocked due to rust in petrol tank getting through the inline fuel filter.

Could be a split pump diaphragm - any sign of petrol leakage from the carb after depressing the accelerator pedal to the floor with engine off?

Could be split 2nd stage pulldown unit diaphragm.

What revs does it happen at (if CL has a rev counter)?

No, you said 'no rev counter'. They're so useful to known which part of carb is in operation.

What speed which gear?

How does the problem resolve itself ?

Stop and wait with engine ticking over (or off) for two minutes then everything is fine?

Is it cold and damp when this happens?

If so, it might be carb icing?

Though I've only had it myself going up a long hill after a cold valley. Not many hills in east anglia.

The pressure drop as air enters the carb venturi forms ice. VW sell a fuel additive to prevent icing or petrol redex would work. Either will clean your carb jets too.

Is the exhaust manifold hot air feed tube present?

How warm is the engine when this occurs? After at least 20 mins driving the gate in the air inlet (waxstat?) will have moved to let cold rather than warmed air in.

But its nearly spring which should be warm enough for it not to happen.

Another idea..

Maybe air leak on a carb vacuum tube or the mounting gasket ?

Could show after a bump.

Are any of the thin rubber tubes to carb cracked?

The one from the distributor to carb for example.

Does the carb waggle on its mount?

Mounting gasket leak can be detected with shaving foam sprayed round the base of a cold carb.

It'll bubble where air's being sucked in.

There's also a temperature dependent valve in the air filter housing that might be suspect as it affects the vacuum to carb though I've never heard anyone else replace one - gsfcarparts do sell 'em (part 18206), so they must fail.

As for the idle revs, when warm there's a screw at the back reachable down a tapering white plastic tube to adjust this. I still can't think why you'd get high idle and occasional loss of power unless just maybe the carb has been set way too rich and an air leak is making the mixture stoich perfect until it gets warm, but I cant quite reconcile that with a working autochoke. But too rich would explain the abominable mileage (I just did 344 miles on 33 litres).

There's also a fast idle speed grub screw on cam-wheel at the front for the auto-choke stops.

The cam-wheel is engaged by pressing the accelerator pedal to the floor and disengaged by the first stage pulldown unit vacuum pulling as the engine fires. That would normally give up to about 2000rpm for the first 5 or so minutes of sedate driving but is metal so normally does not need adjusting.

Edited 14 April, 200818 yr by dvderlm

Presume you have a Pierburg 24/28 2E3 Carb

Hesitation- could be the accelerator pump diaphram spring has lost its tension

Fast idle- the screws inside a long tube and the idle mixture screw is below this near to spring

I think we need some more symptoms.

There aren't really any.

I guess:

It doesn't misfire or cut-out... then I'll stick my neck out and say it's probly not electrical.

I assume:

It's not overheating.

The autochoke works.

No misfire, no stalls/cut-outs. Not overheating, no problems with cold or warm starts, so I presume the autochoke is fine.

What would happen if the autochoke wasn't working properly. I would have thought it would be difficult to start, unless of course it's stuck on (but maybe that would make hot starting tricky?), or would it just make it run very rich? I know that tapping the accelerator is meant to lower the revs once the car's warmed up a bit, but this does nothing in my car.

Could be a carb jet partially blocked due to rust in petrol tank getting through the inline fuel filter.

Could be a split pump diaphragm - any sign of petrol leakage from the carb after depressing the accelerator pedal to the floor with engine off?

Could be split 2nd stage pulldown unit diaphragm.

I don't think it's rust, the fuel filter is clean and shows no signs of any contamination. I haven't had the carb apart or checked it out so can't say about leaks at present

What revs does it happen at (if CL has a rev counter)?

No, you said 'no rev counter'. They're so useful to known which part of carb is in operation.

What speed which gear?

Variable speeds... but usually under acceleration, so throttle fairly open

How does the problem resolve itself ?

I keep on driving, normal service resumes

Stop and wait with engine ticking over (or off) for two minutes then everything is fine?

Is it cold and damp when this happens?

If so, it might be carb icing?

Though I've only had it myself going up a long hill after a cold valley. Not many hills in east anglia.

The pressure drop as air enters the carb venturi forms ice. VW sell a fuel additive to prevent icing or petrol redex would work. Either will clean your carb jets too.

Don't think it's carb icing, it hasn't been that cold around here.

Is the exhaust manifold hot air feed tube present?

How warm is the engine when this occurs? After at least 20 mins driving the gate in the air inlet (waxstat?) will have moved to let cold rather than warmed air in.

Tube present and properly connected. Has happened with the engine cold and warm.

Another idea..

Maybe air leak on a carb vacuum tube or the mounting gasket ?

Could show after a bump.

Are any of the thin rubber tubes to carb cracked?

The one from the distributor to carb for example.

Does the carb waggle on its mount?

Mounting gasket leak can be detected with shaving foam sprayed round the base of a cold carb.

It'll bubble where air's being sucked in.

There's also a temperature dependent valve in the air filter housing that might be suspect as it affects the vacuum to carb though I've never heard anyone else replace one - gsfcarparts do sell 'em (part 18206), so they must fail.

Don't know about these things, I'll check.

As for the idle revs, when warm there's a screw at the back reachable down a tapering white plastic tube to adjust this. I still can't think why you'd get high idle and occasional loss of power unless just maybe the carb has been set way too rich and an air leak is making the mixture stoich perfect until it gets warm, but I cant quite reconcile that with a working autochoke. But too rich would explain the abominable mileage (I just did 344 miles on 33 litres).

There's also a fast idle speed grub screw on cam-wheel at the front for the auto-choke stops.

The cam-wheel is engaged by pressing the accelerator pedal to the floor and disengaged by the first stage pulldown unit vacuum pulling as the engine fires. That would normally give up to about 2000rpm for the first 5 or so minutes of sedate driving but is metal so normally does not need adjusting.

I reckon I did 200 miles on about 25 litres of petrol (filled up this afternoon), which works out at about 36mpg. Not sure if that's good for my car as I don't have any fuel consumption figures, but I reckon it could be better.

Thanks for the help, some food for thought there.

Edited 14 April, 200818 yr by edmundator

With a bust but open autochoke starting would be hard.

With a bust closed autochoke you'd see bad fuel consumption and blue/black smoke from the exhaust.

Take the air filter cover off and watch what the choke butterfly does - it should move from nearly closed to slightly open when engine fires. Then open up as engine warms.

I reckon I did 200 miles on about 25 litres of petrol (filled up this afternoon), which works out at about 36mpg. Not sure if that's good for my car as I don't have any fuel consumption figures, but I reckon it could be better.

36mpg is not bad, but if you're not ragging it, not stuck in queues, not leaking fuel not binding brakes or lugging heavy loads around then I think it could be better. Around town some people report 30mpg. I get 47mpg commuting in winter.

A spare pump diaphragm and/or spring can be got off almost any scrap pierberg carb, eg Golf or even Ford Sierra upto 1991-ish.

Could it be something blocking a jet?, I had a problem with my MK2 that something was blocking a jet and at random times it would lose power and almost lurch forward then be ok again. The only way to solve this was to take the carb off, take it appart and clean it all out.

Also I remember mine idled high at times, causing it be rich. Again a carb problem, then cleared itself after the driving got going. The only way I think it can get sortted is fettle and fettle some more with the carb until you get the right settings as I found out and the new owner found out too lol.

Cheers